To date, digital television broadcasting in which plural pieces of information can be transmitted at the same time (hereinafter referred to simply as “digital broadcasting”) has attracted attention as a form of digital broadcasting, and this has already been put to practical use as digital broadcasting using satellites. Further, it is anticipated that, in the future, there will coexist various digital broadcasts using different transmission forms by different broadcast providers, such as digitized ground wave television broadcasts and digital satellite broadcasts by different broadcast providers. However, a digital broadcast data receiving apparatus for receiving digital broadcasts (hereinafter, referred to simply as “receiving apparatus”) has a large circuit scale and so the size of the receiving apparatus itself is large. Further, the receiving apparatus is expensive because it is composed of many parts. So, in the case where many digital broadcasts coexist, it is desired that a single receiving apparatus can receive plural digital broadcasts.
Generally, digital broadcasting employs a packet mode data transmission method based on the MPEG (Moving Picture Experts Group) system standard, which is an international standard. In this method, to avoid illegal viewers, program broadcast data relating to program broadcasts, such as video and audio data, are encoded.
Further, in contrast with the conventional analog broadcasting, other data required for receiving program broadcasts (hereinafter referred to simply as “required data”) are multiplexed with the program broadcast data to be transmitted. For example, program tables, mails to the viewer, and entitlement management messages (hereinafter referred to as “EMM”) such as key information for decoding are multiplexed with the program broadcast data.
Since it is not known in advance when the data like the key information for decoding or the mail to the viewer, which is to be received even when the viewer does not watch the program, is actually transmitted, the receiving apparatus must receive the program broadcast continuously, whether the viewer watches the received program broadcast or not.
Further, since it is not known when the updating of the program table data is performed, the receiving apparatus must continuously receive the program table data which is included in the required data that is multiplexed in the digital broadcast data. When it is received, the program table data stored in the receiving apparatus should be immediately updated.
Moreover, when a lot of digital broadcasts coexist, it is desired that, while the viewer watches a program, the receiving apparatus receives and records another program which is broadcast on a different channel in the same period of time.
To be specific, as long as a digital VTR is able to receive a digital broadcast, record the received digital broadcast data in a recording medium, and playback the recording medium in which the digital broadcast data is recorded, this digital VTR can obtain the information to be received (e.g., a mail to the viewer which is broadcast in a satellite broadcast or the like, key information for decoding, which is required when the viewer resumes watching the digital broadcast transmitted after playback of the digital VTR has ended, etc.) while reproducing the digital broadcast data recorded in the recording medium.
However, existing receiving apparatus are designed so as to receive only one broadcast and, therefore, they cannot receive another broadcast simultaneously with the broadcast being received.
So, in designing a receiving apparatus which can receive a plurality of digital broadcasts at the same time, it is desired that the receiving apparatus can obtain various kinds of information multiplexed in a digital broadcast (a first broadcast) which are desired by the viewer or required to be obtained even when the viewer does not watch the broadcast, while the viewer watches another digital broadcast (a second broadcast). Thereby, when the viewer resumes watching the first broadcast which has been interrupted because the viewer has watched the second broadcast, it is avoided that information required for the first broadcast is insufficient or that information transmitted as a mail is missed.
Further, in the case of the above-mentioned digital VTR, it is considered to construct a receiving apparatus which receives a plurality of digital broadcasts from different channels or different providers, or a plurality Of digital broadcast data from different input sources such as digital VTRs, by integrating circuits of receivers each receiving a digital broadcast from a channel or a provider, or circuits for processing program data taken from data reproduced by the digital VTRs.
In the case of analog broadcasting, since an analog broadcast receiving apparatus can be designed in a relatively simple circuit construction, the size of the apparatus itself is not so large, and it is easy to integrate plural receivers in one analog broadcast receiving apparatus. So, the cost of the apparatus can be reduced. However, in the case of a digital broadcast data receiving apparatus, if plural receivers are simply integrated, the cost of the receiving apparatus increases with the number of the receivers since the construction of each receiving circuit is complicated. In this case, the circuit scale and the cost of the receiving apparatus are equivalent to those in the case of buying a plurality Of receivers for the respective broadcasts (channels or providers). Furthermore, since the circuit scale increases, the size of the receiving apparatus itself increases with the number of digital broadcasts to be received.